meso-Pyrrolyl boron dipyrromethene (BODIPY) was prepared under simple reaction conditions by using commercially available chemicals. Prior to this work, the BODIPY compound was prepared in multiple steps by using precursors which were not readily available. The X-ray structure of BODIPY revealed that the meso-pyrrole ring is tilted towards the BF2-dipyrrin moiety with a dihedral angle of 33.94°. The reactivity of the meso-pyrrole ring of BODIPY was tested by subjecting it to bromination and formylation reactions, which afforded (α-bromopyrrolyl) BODIPY and (α-formylpyrrolyl) BODIPY in decent yields. The (α-formylpyrrolyl) BODIPY was used to prepare the pyrrole bridged BODIPY dyad. The pyrrole bridged BODIPY dyad exhibited a 15-20 nm bathochromic shift in the absorption band and was weakly fluorescent compared to meso-pyrrolyl BODIPY. Furthermore, our studies show that the meso-pyrrolyl BODIPY can be used as a specific sensor for F(-) ions because of the presence of meso-pyrrole NH which is involved in interactions with F(-) ions. To prove that meso-pyrrole NH is involved in sensing F(-) ions, we also prepared meso-(N-methylpyrrolyl)-BODIPY and characterized it by various spectroscopic techniques and crystallography. Our studies reveal that meso-(N-methylpyrrolyl)-BODIPY does not sense F(-) ions, supporting the involvement of meso-pyrrole NH in sensing F(-) ions.
The oxasmaragdyrins containing one five membered heterocycle such as pyrrole, thiophene and furan in place of one of the meso-phenyl group were synthesized by acid-catalyzed oxidative coupling reaction of meso-heterocycle substituted dipyrromethane with 16-oxatripyrrane in the presence of catalytic amount of trifluoroacetic acid followed by oxidation with DDQ. The smaragdyrin macrocycles containing one fivemembered heterocycle at meso-position were characterized by HR-MS and detailed 1D and 2D NMR studies. The absorption and fluorescence studies revealed that the presence of five membered heterocycle at mesoposition of smaragdyrin resulted in bathochromic shifts in absorption and emission bands with slight reduction in quantum yields compared to smraragdyrin macrocycle containing six membered meso-phenyl groups. The electrochemical studies revealed that the meso-heterocycle smaragdyrins are electron deficient compared to meso-phenyl smaragdyrins.
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